To troubleshoot, remove the redirect from UE, change:
$GoToPage = "thank-you.html"
$GoToPage = ""
Then add the following code in the body tag:
<?php @session_start(); var_dump($_SESSION); ?>
this will write the session contents to the page including the status of passing the email to the SMTP server. If the status says the email was successfully passed to the SMTP server, you will need to contact the host to determine why the SMTP server is not relaying the email to the recipient.